Plone.app.collection in Plone 5.2? Where is it?

I am confused about plone.app.collection. There are various references in Plone 5.2 to plone.app.collection both in the code and in the documentation but there is no such package in a decent 5.2 buildout!? Anything I am missing?

plone.app.collection is Archetypes only. Collections are part of plone.app.contenttypes as a behavior and a content-type that implements this behavior.

Plone Foundation Code of Conduct